The present invention relates to a fuel cell humidification apparatus for the humidification of gases which are supplied to electrodes of a fuel cell of the solid polymer type.
Generally, hydrogen can be generated by reforming hydrocarbon or methanol. Hydrogen thus generated is applicable to fuel cells.
Such a type of fuel cell includes one known in the art as the solid polymer type (see for example Japanese Unexamined Patent Gazette No. H11-67256). This solid polymer type fuel cell comprises a hydrogen electrode (as a fuel electrode) and an oxygen electrode (as an air electrode) between which is interposed a solid polymer electrolyte, wherein hydrogen containing reformed gas as the fuel and oxygen containing air (which is oxygen containing gas) are supplied to the hydrogen electrode and to the oxygen electrode, respectively, to create electromotive force between the electrodes.
In such a solid polymer type fuel cell, it is required that the electrolyte be kept moist by water for reducing proton conduction resistance in the electrolyte, and hydrogen containing reformed gas and oxygen containing gas are supplied, almost in a state of water vapor saturation.
In order to place reformed gas and air in such a state, for the case of the reformed gas, water vapor is introduced during its generation so that it holds moisture. The amount of heat necessary for obtaining water vapor that is added to the reformed gas during generation thereof is afforded by reformed gas sensible heat or by combustion heat resulting from combustion of fuel cell exhaust gas by burner.
On the other hand, for the case of the air that is supplied to the oxygen electrode of the fuel cell, fuel cell cooling water is used to humidify the air within the fuel cell and the amount of heat necessary for such humidification is afforded by fuel cell exhaust heat.
However, since the amount of heat necessary for obtaining water vapor that is added to reformed gas and air is afforded by reformed gas sensible heat, fuel cell exhaust gas combustion heat, or fuel cell exhaust heat, this essentially requires a supply of heat, and improvements are desirable to increase the thermal efficiency of fuel cell systems.
Bearing in mind the above, the present invention was made. Accordingly, an object of the present invention is to improve the thermal efficiency of a fuel cell system by making good utilization of fuel cell exhaust gas for humidifying gases such as reformed gas to the fuel cell without having to provide heating necessary for obtaining water vapor.
Attention was directed to the fact that fuel cell exhaust gases contain therein water vapor and, more specifically, in accordance with the present invention, water vapor contained in the fuel cell exhaust gas penetrates through a water vapor permeable membrane and then supplied to gas such as reformed gas in order to achieve the foregoing object.
More specifically, a humidification means (31) is provided to a fuel cell (1) having oxygen and hydrogen electrodes between which is interposed a solid polymer electrolyte for producing an electromotive force between the electrodes by supplying hydrogen containing reformed gas reformed in a reformation means (4) and oxygen containing gas to the hydrogen electrode and to the oxygen electrode, respectively, whereby water vapor contained in exhaust gas expelled from the fuel cell (1) penetrates through a water vapor permeable membrane (34) so that the water vapor is supplied, at least, to supply gas to the reformation means (4).
In accordance with such an arrangement, by virtue of the humidification means (31), water vapor contained in exhaust gas drawn out of the fuel cell (1) passes through the water vapor permeable membrane (34) so that it is supplied, at least, to gas to the reformation means (4). This humidifies, almost to water vapor saturation, reformed gas that is supplied to the hydrogen electrode of the fuel cell (1), and a supply of heat for such humidification is made unnecessary. Consequently, it is possible to improve the thermal efficiency of a fuel cell system.
Further, the reformation means (4) may include a partial oxidation reformation section (6) which generates, from source gas, hydrogen rich reformed gas through reactions including partial oxidation.
Further, the humidification means (31) may be arranged so that water vapor contained in hydrogen electrode exhaust gas expelled from the hydrogen electrode of said fuel cell (1) penetrates through the water vapor permeable membrane (34) and then supplied either to air or to a mixture of air and source gas that is introduced into the partial oxidation reformation section (6).
As a result of such arrangement, reformed gas that is supplied to the hydrogen electrode of the fuel cell (1) is humidified by the passage of water vapor contained in hydrogen electrode exhaust gas of the fuel cell (1) through the water vapor permeable membrane (34), thereby improving the thermal efficiency of a fuel cell system.
On the other hand, the reformation means (4) may include a water vapor reformation section (43) which generates, from source gas, hydrogen rich reformed gas through reactions.
Further, the humidification means (31) may be arranged so that water vapor contained in hydrogen electrode exhaust gas expelled from the hydrogen electrode of said fuel cell (1) penetrates through the water vapor permeable membrane (34) and then supplied to source gas that is introduced into the water vapor reformation section (43).
As a result of such arrangement, reformed gas that is supplied to the hydrogen electrode of the fuel cell (1) can be humidified by the passage of water vapor contained in hydrogen electrode exhaust gas of the fuel cell (1) through the water vapor permeable membrane (34), thereby improving the thermal efficiency of a fuel cell system.
The humidification means (31) may include a first humidification section (32) which humidifies air or gas with water vapor in hydrogen electrode exhaust gas and a second humidification section (36) which humidifies the air or gas humidified in the first humidification section (32) with water vapor resulting from permeation of heated hot water through a water vapor permeable membrane (38).
As a result of such arrangement, air or gas is humidified by the passage of water vapor in hydrogen electrode exhaust gas through the water vapor permeable membrane (34) in the first humidification section (32). The air or gas is further subjected to humidification by water vapor resulting from permeation of heated hot water penetrating through the water vapor permeable membrane (38) in the second humidification section (36). Such two-stage air (or gas) humidification provides stable humidification of the reformed gas even when the fuel cell (1) undergoes a change in its load.
The humidification means (31) may be arranged so that water vapor contained in oxygen electrode exhaust gas expelled from the oxygen electrode of the fuel cell (1) penetrates through the water vapor permeable membrane (34) and then supplied to oxygen containing gas to the fuel cell (1).
As a result of such arrangement, oxygen containing gas that is supplied to the oxygen electrode of the fuel cell (1) is humidified by the passage of water vapor in oxygen electrode exhaust gas of the fuel cell (1) through the water vapor permeable membrane (34). Also, in this case it is possible to improve the thermal efficiency of a fuel cell system.
In such a case, the humidification means (31) may include a first humidification section (33) which humidifies gas with water vapor in oxygen electrode exhaust gas and a second humidification section (37) which humidifies the gas humidified in the first humidification section (33) with water vapor resulting from permeation of heated hot water through the water vapor permeable membrane (38).
As a result of such arrangement, oxygen containing gas is humidified by the passage of water vapor in oxygen electrode exhaust gas through the water vapor permeable membrane (34) in the first humidification section (33). Thereafter, the oxygen containing gas is further humidified by water vapor resulting from permeation of heated hot water through the water vapor permeable membrane (38) in the second humidification section (37). Because of such two-stage oxygen containing gas humidification, it is possible to achieves stable oxygen containing gas humidification even when the fuel cell (1) undergoes a change in its load.
The humidification means (31) may be arranged so that water vapor contained in oxygen electrode exhaust gas expelled from the oxygen electrode of the fuel cell (1) penetrates through the water vapor permeable membrane (34) and then supplied either to air or to a mixture of air and source gas that is introduced into the partial oxidation reformation section (6).
As a result of such arrangement, reformed gas that is supplied to the hydrogen electrode of the fuel cell (1) is humidified by the passage of water vapor contained in oxygen electrode exhaust gas of the fuel cell (1) through the water vapor permeable membrane (34), thereby improving the thermal efficiency of a fuel cell system.
The humidification means (31) is arranged so that water vapor contained in oxygen electrode exhaust gas expelled from the oxygen electrode of said fuel cell (1) penetrates through the water vapor permeable membrane (34) and then supplied to source gas that is introduced into the water vapor reformation section (43).
Also, as a result of such arrangement, reformed gas that is supplied to the hydrogen electrode of the fuel cell (1) is humidified by the passage of water vapor contained in oxygen electrode exhaust gas of the fuel cell (1) through the water vapor permeable membrane (34), thereby improving the thermal efficiency of a fuel cell system.
In such a case, the humidification means (31) includes a first humidification section (33) which humidifies air or gas with water vapor in oxygen electrode exhaust gas and a second humidification section (37) which humidifies the air or gas humidified in the first humidification section (33) with water vapor resulting from permeation of heated hot water through the water vapor permeable membrane (38).
As a result of such arrangement, air or gas is humidified in the first humidification section (33) by the passage of water vapor in oxygen electrode exhaust gas through the water vapor permeable membrane (34) and thereafter further humidified in the second humidification section (37) by water vapor resulting from permeation of heated hot water penetrating through the water vapor permeable membrane (38). Such a two-stage air (or gas) humidification makes it possible to achieves stable reformed gas humidification even when the fuel cell (1) undergoes a change in its load.
Further, the humidification means (31) is arranged so that water vapor contained in hydrogen electrode exhaust gas expelled from the hydrogen electrode of the fuel cell (1) penetrates through the water vapor permeable membrane (34) and then supplied to oxygen containing gas to the fuel cell (1).
As a result of such arrangement, oxygen containing gas that is supplied to the oxygen electrode of the fuel cell (1) is humidified by water vapor in hydrogen electrode exhaust gas of the fuel cell (1), thereby improving the thermal efficiency of a fuel cell system.
In such a case, the humidification means (31) includes a first humidification section (32) which humidifies gas with water vapor in hydrogen electrode exhaust gas and a second humidification section (36) which humidifies the gas humidified in the first humidification section (32) with water vapor resulting from permeation of heated hot water through the water vapor permeable membrane (38).
As a result of such arrangement, oxygen containing gas is humidified in the first humidification section (32) by the passage of water vapor in hydrogen electrode exhaust gas through the water vapor permeable membrane (34) and thereafter further humidified in the second humidification section (36) by water vapor resulting from permeation of heated hot water. Such two-stage oxygen containing gas humidification makes it possible to achieve stable oxygen containing gas humidification even when the fuel cell (1) undergoes a change in its load.
The humidification means (31) may be formed integrally with said fuel cell (1). As a result of such arrangement, the humidification section (31) is incorporated into the fuel cell (1), thereby making it possible to provide a simplified, compact structure for fuel cell systems.
An arrangement may be made in which the first and second humidification sections (32), (33), (36) and (37) of the humidification means (31) are formed integrally with the fuel cell (1) and the heated hot water is cooling water for said fuel cell (1).
As a result of such arrangement, it becomes possible to utilizes existing cooling water as the heated hot water as well as to provide a simplified, compact structure for fuel cell systems while achieving stable humidification of the gas to the fuel cell (1).
Alternatively, an arrangement may be made in which the first and second humidification sections (32), (33), (36) and (37) of the humidification means (31) are provided separately from the fuel cell (1) and the heated hot water is hot water for a hot water supply means (16). As a result of such arrangement, the heated hot water can be embodied.
The water vapor permeable membrane (34), through which water vapor contained in exhaust gas penetrates, is a hydrophilic membrane. Alternatively, the water vapor permeable membrane (34), through which water vapor contained in exhaust gas penetrates, is a polymer membrane having a sulfonic acid group.
Such arrangement provides the water vapor permeable membrane (34) suitable for allowing the passage of water vapor contained in exhaust gas of the fuel cell (1).
The water vapor permeable membrane (38) of each of the second humidification sections (36) and (37) is a hydrophobic porous membrane. Further, the water vapor permeable membrane (38) of each of the humidification sections (36) and (37) is a porous membrane formed from a porous membrane of the polytetrafluoropolyethylene family, the polypropylene family or the polyethylene family.
Such arrangement provides the water vapor permeable membrane (38) suitable for allowing the passage of water vapor from heated hot water.